Monday, April 30, 2007

High-throughput AFEX pretreatment screening on poplar

Venkatesh Balan, Derek Marshall, Shishir P. S. Chundawat, and Bruce E. Dale. Department of Chemical Engineering and Material Science, Michigan State University, 2527 Engineering building, E. Lansing, MI 48824

Conversion of plant biomass to liquid fuels is an attractive means of reducing petroleum dependency.  Among the various sources of biomass, hybrid poplar (Populus nigra x Populus maximowiczii) is of interest due to its wide availability and high density that reduces the cost of transport and improves storability and for its high glucan (~ 45%) and xylan (~ 18%) content. However, we observe considerable poplar recalcitrance toward enzymatic hydrolysis. Using our 300 mL, #316 stainless steel AFEX reactor, even with higher severity conditions (180 oC, 1:1 ammonia to biomass loading) the glucan conversion was found to be 50% for 15 FPU of celluase loading per gram of glucan compared to 5% for untreated poplar.  With higher ammonia to biomass ratios we observed some improvements in conversion. However, there are significant experimental limitations for us at higher temperatures with our old AFEX reactor system, including slow heat transfer rates and possible formation of enzyme inhibitors. With the recent development of our high-throughput AFEX reactor system, we can study five sets of reaction conditions simultaneously. In addition, the new reaction volume is 22 ml, thereby reducing heat transfer problems. Also, we have much greater flexibility in mixing and heating ammonia and water prior to reacting them with the biomass. We report improvements in glucan conversion by varying AFEX conditions.  Formation of inhibitors will also be discussed. This research is performed as part of the Consortium for Applied Fundamentals and Innovation (CAFI) biomass conversion project.